Device for avoiding short circuit damage in electrolytic cells



June 14, 1966 J. Di'DRFEL ETAL I 3, 56,

DEVICE FOR AVOIDING SHORT CIRCUIT DAMAGE IN ELECTROLYTIC CELLS FiledOct. 24,1961

mvsm'gns JOHA N/vEs DORFEL FRANZ HOLZ/NGER HEINZ .SCHM/DT WERNER SCHMIDTWALDEMAR Z/EMER ATTORN' s United States Patent many Filed Oct. 24, 1961,Ser. No. 147,325

Claims priority, application Ggrmauy, Oct. 29, 1960,

6 Claims. (Cl. 204-228) The present invention relates to a process anddevice for avoiding short'circuit damage in electrolytic cells.

Nowadays in the field of electrolysis of alkali metal chlorides thetrend is to construct larger units for electrolysis, since, as comparedwith smaller units, they have a number of advantages, for example lowerconstruction costs, better controlabili-ty of the total unit, andsmaller number of individual parts.

Mercury cells, of a'llthose of horizontal construction, are superior todiaphragm cells. The largest diaphragm cells used in industry are mostlyoperated at a current intensity of about 30,000 amperes, while mercurycells are frequently operated at 100,000 to 200,000 amperes.

Because of the high current intensity ofmodern mercury cells inoperation with minimum voltage, i.e. smallest electrode distance, andwith the use of large anodes, the 1 short circuits occurring between theelectrodes, which tend to occur particularly when the current intensityvaries considerably or with circulation failures in the cell, forexample owing to an electrode fracture, gain more and more importanceand are today" a more serious problem than in the past. This problemisespecially serious in modern units with well designed lowering,deyices for the anodes in which, in order to minimize power losses, theelectrode distance is as small as possible and kept practically constantover the whole period of operation of the cell. The seriousness of thisproblem is further increased by the fact that short circuits occurringin electrolytic cells operated with very high current intensities maycause considerable damage.

The detrimental Joules heat occurring between an anode and the cathodeas a result of a short circuit could be used, for example by means of athermo-element (bimetal) measuring the temperature, to cut oil?electrically or mechanically the current supply to the anode by acontrol element, but devices. of this kind would be very complicated andthus uneconomical'and unsuited for industrial use.

It would be likewise too expensive, complicated, and unsatisfactory touse the considerable current increase occurring in a short circuit toactuate a suitable control element via an ampere meter.

Now, we have found a process which avoids short circuit damage inelectrolytic cells, especially in horizontal mercury cells used for theelectrolysis of alkali met-a1 chlorides, and does not show the abovedisadvantages.

The process of the invention enables electrolytic cells to be safelyoperated with very high current intensity in a simple and economicalmanner. The Ioules heat occurring in the anode bar as a result of ashort circuit is used for melting an alloy that is fusible at atemperature in the range from about 80 C. to 180 C., preferably 100 C.to 140 C., and, under normal conditions of electrolysis, holds togethertwo metal parts in the form of a soldered joint. By spring power the twometal parts are then automatically separated and the current supply isinstantaneously interrupted.

A further object of the present invention is to provide a device forcarrying out the above process. The current lead to the anode shaft isprovided on the other end with a metal part comprising a plug. The plugis soldered into a recess of a second metal part by means of an alloy,said second metal part being attached to the current supply guides ofthe electrolytic cells. The Joules heat occurring between the anode andthe cathode as a result of a short circuit melts the alloy before damagecan occur. The current lead is connected with the anode support .by aspring which is insulated to prevent current from blowing through it.

In the accompanying drawings, FIGURES 1-4 diagrammatically represent byway of example a suitable embodiment of the device of the invention.FIGURE 1 illustrates the whole device and the parts of an electrolytic,cell directly connected therewith, and FIGURES 2-4 show,

on an enlargedscale, the essential parts of the device. In FIGURES 1-4numeral 1 is a copper rod, 2 is the current lead connected therewith, 4is the metal part pro- 12 represents the soldered joint between thecopper rod and anode shaft 13, 14 is the cover of theel ectrolytic cell,15-designates the anode block of graphite directly above the mercurycathode, and 16 is the soldered joint holding together met-a1 parts 4and 7 and which is melted by the heat accumulation resulting from ashort circuit.

, FIGURES 3 and 4 show, by way'of example, a suitable form of metalparts 7 and 4, on an enlarged scale.

In the device of the invention it is of advantage to join parts 4 and 7by soldering plug 3 into recess 6 with an alloy having a melting pointin the range from C. to 180? C.', and preferably C. to C. Especiallysuitable are lloys of lead, tin, antimony, bismuth and the like. Allother metal par-ts of the anode supply are prefer-ably made of copper.

Currentle'ad 2 is suitably made of copper bands in sandwich form.

-In order to better accumulate the Joules heat pro duced in a shortcircuit in the immediate neighbourhood of soldering joint 16, it isadvantageous to reduce the cross section of metal part 7 near thesoldering joint, for example by a contraction 11.

The function of the device of the invention shown in FIGURES 1-4 is verysimple. The Joules heat occurring in a high current flow short circuitwhich may damage the electrolytic cell melts at soldering point 16 themetal alloy connecting metal parts 4 and 7, and the currentinsulatedspring 9, fastened between the current lead 2 and the anode support 10,pulls plug 3 of metal part 4 fixed to the current lead out of recess 6of metal part 7 and thus interrupts at once automatically the currentsup- -two metal parts 4 and 7 is enhanced by the fact that the reducedcross section of plug 3 provides a higher current density at thesoldering point so that in the case of a high short circuit current ahigher Joules heat is produced at this point. With a normal currentintensity in the cell the voltage loss at the soldering joint is so lowthat it can be neglected.

In case the copper rod 1 is soldered into graphite shaft 13 (solderingpoint 12) metal parts 4 and 7 must be soldered by an alloy which has alower melting point than the alloy used for soldering joint 16. When,for example,

copper rod 1 is soldered into graphite anode shaft 13 with an alloy'thatmelts atabout 180 C., an alloy having a.

melting point of 80 C. to at most 180 C. and preferably of about 120 C.is advantageously used for soldering joint 16.

The alloy connecting metal parts 4 and 7 has a melting point such thatthe melting time on the occurrence of a short circuit is as short aspossible, depending on the local conditions. This is particularlyfavored by the increase of the current density due to the reduction insize of plug 3 and recess 6.

The advantage of the safety fuse of the present invention resides in thefact that the individual parts are very simple and readily available,and that plug 3 can be soldered into recess 6 very quickly and easily.After having eliminated the cause of the short circuit, the individualparts are ready for re-use, and plug 3 of metal part 4 is again solderedwith the alloy concerned into recess 6. The shape of parts 7 and 4 shownin FIGURES 3 and 4 provides an especially good soldered joint. Recess 6of part 7 is filled with solder and plug 3 of part 4 is then introducedinto the filled recess. After cooling and solidifying of the solder, andafter having fastened current lead 2 to metal part 4, the safety fuse isagain ready for use.

By the rapid interchange of the main parts of the device of theinvention with a stock of ready soldered reserve parts, short circuitdamage can be avoided with reliability in modern large electrolyticce'lls.

. We claim: 1. In an electrolytic cell having an anode and a source ofelectric current for said anode,-a reusable fuse for making are-formable connection of said source to said anode and automaticallydisconnecting said source from said anode when there is a short circuitwhich comprises a flexible current lead conected to the anode at one endand having at its other end aconducting member with a plug portion, asecond conducting member connected to the source of electrical energyand having a recess engageable by said plug, said plug being retained insaid recess for conducting an electrical current of preselected maximumintensity from said source to said anode by an alloy solder having apreselected melting point,.said alloy solder comprising the sole meansphysically securing said receiving member to said plug member, at leastone of said plug portion andsaid second conducting member having across-sectional area adjacent said solder substantially less than theminimum cross-sectional area of said flexible current lead, and springmeans for withdrawing the plug from the recess upon melting of the alloysolder.

2. A device as claimed in claim 1, wherein the alloy used for solderingthe plug into the recess of the metal part has a melting point in therange from about 80 C. to 180 C.

3. A device as claimed in claim 1, wherein the current leadto the copperrod is composed of copper bands in sandwich form.

4. A device as claimed in claim 1, wherein for obtaining a better heataccumulation the second metal part has a reduced cross section near thesoldering point.

5. In an electrolytic cell having a pair of electrodes adapted to beenergized by high-current electrical supply means, reusable fuse meansfor providing a reformab'le conductive connection between one of saidelectrodes and said supply means and automatically breaking saidconnection when a short-circuit is created between said electrodes, saidfuse means comprising, in combination, a conductor conductivelyconnected to said one electrode and having a plug member at one end, aconductive receiving member conductively connected to said supply meansand having a recess adapted to receive said plug member, and a quantityof alloy solder in said recess securing said plug member to saidreceiving member, said alloy solder comprising the sole means physicallysecuring said receiving member to said plug member, at least one of saidplug member and said receiving member having a crosssectional areaadjacent said quantity of solder substantially less than the minimumcross-sectional area of said conductor so as to accelerate the heatingand melting of said solder and free said members from one another whenshort-circuit currents flow through said one member, saidcross-sectional area of said one member being suflicient to preventmelting of said solder when the current flow through said one member isless than a predetermined maximum value.

6. Apparatus as in claim 5 including means biasing said plug member awayfrom said receiving member so as to automatically separate said memberswhen said solder melts.

References Cited by the Examiner UNITED STATES PATENTS JOHN H. MACK,Primary Examiner. JOHN R. SPECK, Examiner.

B. JOHNSON, H. S. WILLIAMS, W. VAN SISE,

Assistant Examiners.

1. IN AN ELECTROLYTIC CELL HAVING AN ANODE AND A SOURCE OF ELECTRICCURRENT FOR SAID ANODE, A REUSABLE FUSE FOR MAKING A REFORMABLECONNECTION OF SAID SOURCE TO SAID ANODE AND AUTOMATICALLY DISCONNECTINGSAID SOURCE FROM SAID NODE WHEN THERE IS A SHORT CIRCUIT WHICH COMPRISESA FLEXIBLE CURRENT LEAD CONNECTED TO THE ANODE AT ONE END AND HAVING ATITS OTHER END A CONDUCTING MEMBER WITH A PLUG PORTION, A SECONDCONDUCTING MEMBER CONNECTED TO THE SOURCE OF ELECTRICAL ENERGY ANDHAVING A RECESS ENGAGEABLE BY SAID PLUG, SAID PLUG BEING RETAINED INSAID RECESS FOR CONDUCTING AN ELECTRICAL CURRENT OF PRESELECTED MAXIMUMINTENSITY FROM SAID SOURCE TO SAID ANODE BY AN ALLOY SOLDER HAVING APRESELECTED MELTING POINT, SAID ALLOY SOLDER COMPRISING THE SOLE MEANSPHYSICALLY SECURING SAID RECEIVING MEMBER TO SAID PLUG MEMBER, AT LEASTONE OF SAID PLUG PORTION AND SAID SECOND CONDUCTING MEMBER HAVING ACROSS-SECTIONAL AREA ADJACENT SAID SOLDER SUBSTANTIALLY LESS THAN THEMINIMUM CROSS-SECTIONAL AREA OF SAID FLEXIBLE CURRENT LEAD, AND SPRINGMEANS FOR WITHDRAWING THE PLUG FROM THE RECESS UPON MELTING OF THE ALLOYSOLDER.